Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'stable/danube'
  - Yardstick: User interface for Yardstick.

    Currently Yardstick doesnt have any UI which gives detail analysis
    of the test-results.
    This commit generates a HTML page after the execution of a command
    "yardstick report generate <task-ID> <TC-name>" which intern
    can be executed after the execution of test-case.
    Used: Highcharts.js for the graphs.

    JIRA: YARDSTICK-280

    Change-Id: Ic98cc348719f3922bff178f52e7944a4a931763a
    Signed-off-by: Rajesh K <4k.rajesh@gmail.com>
    (cherry picked from commit 25b21add71fcf7c2c795bd950b5117d69fac68fb)